• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.198-201
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• 2001

Porous structures of aluminum foam have been studied by using return aluminum scrap. The apparent foam shape, foam height, density, pore size and their distributions in various section areas of the experimental samples have been investigated. The sample have been cast into metallic mold, using aluminum foam prepared from a precursor based on pure Al ingot and return aluminum scrap mixed with various amounts of 1-2wt% increasing viscosity and foam agent materials. The process provides for flexibility in design of foam structures via relatively easy control over the amount of hydrogen evolution and the drainage processes which occur during foam formation. This is facilitated by manipulating parameters such as the foaming agent, thermal histories during solidification and mix melt viscosities. A metal for producing the foamed are decomposing a foaming agent in a molten metal such that there is an initial and a subsequent expansion due to foaming agent. It has been found that the Al porous foaming with variation amount of 1∼2wt% foam agent and at 2min holding time, which melting temperature has appeared homogeneous pore size at 650∼700$^{\circ}C$. The compression strength were 10-13 kg/min at 125ppi, and increased by higher pore density. The acoustical performance of the panel made with the foamed aluminum is considerably improved; its absorption coefficient shows NRC 0.6-0.8. It has been found that the Al foam is very preferable for the compactness of the thermal system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.5
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• pp.551-557
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• 2014

This paper presents a robust lateral controller for autonomous guidance of a farm tractor in field operations. Although mechanical steering actuators have recently been used for passenger vehicles, the steering actuator of the farm tractor is based on a hydraulic system, resulting in limited bandwidth and a larger time delay. Based on a kinematic tractor model with steering actuator dynamics, a nonlinear control technique called dynamic surface control is applied to design a robust lateral controller that compensates for uncertainty owing to steering actuator and road geometry. Finally, tracking performance and robustness of the proposed controller are validated via commercial tractor simulations, with respect to the time delay of the steering actuator and road geometry (e.g., up and down hills), on a given field with a constant friction coefficient.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.6
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• pp.3698-3707
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• 2015

In this study, wet surface heat transfer and friction characteristics of non-symmetric slit-finned heat exchangers are experimentally investigated. Louver-finned heat exchangers are also tested for comparison purpose. The effect of fin pitch on j and f factor is negligible. Louver fin samples yield higher j and f factors than slit fin samples. For one row, j and f factors of louver fin are 27% and 31% higher than those of slit fin. For two row, j and f factors of louver fin are 15% and 30% higher. Both j and f factor decrease as the number of tube row increases. For one row, average j/f ratios of slit fin samples are 3.4% larger than those of louver fin samples. For two row, average j/f ratios of slit fin samples are 11.5% larger. A new correlation was developed using the present data.

• Journal of the Korean Geotechnical Society
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• v.37 no.6
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• pp.39-50
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• 2021

Recently, as the occurrence of earthquakes with a magnitude of 5.0 or higher in Korea increases, many studies and interests in seismic design are increasing. A lot of damage was caused by the Pohang earthquake in 2017, and port facilities such as a breakwater were also damaged. This study analyzed the dynamic behavior of the upright breakwater, an external facility, based on a centrifugal model experiment. A series of centrifugal model test was conducted by three different seismic waves such as Pohang Earthquake Wave, Artificial Wave I, and II. As a result, the dynamic behavior of upright breakwater was analyzed. The review showed that acceleration amplification tends to be suppressed as breakwater foundation ground increases support and stiffness through DCM reinforcement and riprap replacement.

• Journal of Korea Water Resources Association
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• v.38 no.10 s.159
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• pp.895-906
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• 2005

The diversity of observed hydrologic data and the development of geographic information system leads significant progress for developing distributed runoff models in the world. One of the typical examples is TOPMODEL, but the spatial coverage of its application Is limited on small headwater basins. The purpose of this study attempts to overcome its limitation and consequently develops a semi-distributed TOPMODEL. The developed model is composed of two components: a watershed runoff component for a lumped representation of hydrologic runoff process on the catchment scale and a kinematic wave type hydraulic channel routing component lot routing the catchment outflows. The application basin is the $2,703km^2$ upper Soyang dam site and several daily and hourly events are selected for model calibrations and verifications. The model parameters are estimated on 1990 daily event. The model performance on correlation coefficient between observed and computed flows are above 0.90 for the verification events. It is concluded that the developed model in this study can be used for flood analysis in large drainage basins.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.9
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• pp.5778-5788
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• 2015

In this study, wet surface heat transfer and friction characteristics of compound enhanced fin-and-tube heat exchangers were experimentally investigated. Louver-finned heat exchangers were also tested for comparison purpose. The effect of fin pitch on j and f factor was negligible. Both j and f factor decreased as number of tube row increased. Compound enhanced fin samples yielded higher j and f factors than louver fin samples. For one row, j and f factors of compound enhanced fin samples were 11% and 43% higher than those of louver fin samples. For two row, those were 8% and 50%, and for three row, those were 17% and 53%. Heat transfer capacities at the same pressure drop of the compound enhanced fin samples were 2.0% for one row, 3.1% for two row and 8.4% for three row larger than those of louver fin samples, Data were compared with predictions of existing louver fin correlations.

• Journal of Ceramic Processing Research
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• v.13 no.spc2
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• pp.328-331
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• 2012

With the recent development of super-precision optical instruments, camera modules for devices, such as portable terminals and digital camera lenses, are increasingly being used. Since an optical lens is usually produced by high-temperature compression molding methods using tungsten carbide (WC) alloy molding cores, it is necessary to develop and study technology for super-precision processing of molding cores and coatings for the core surface. In this study, Rhenium-Iridium (Re-Ir) thin films were deposited onto a WC molding core using a sputtering system. The Re-Ir thin films were prepared by a multi-target sputtering technique, using iridium, rhenium, and chromium as the sources. Argon and nitrogen were introduced through an inlet into the chamber to be the plasma and reactive gases. The Re-Ir thin films were prepared with targets having a composition ratio of 30 : 70, and the Re-Ir thin films were formed with a 240 nm thickness. Re-Ir thin films on WC molding core were analyzed by scanning electron microscope (SEM), atomic force microscope (AFM), and Ra (the arithmetical average surface roughness). Also, adhesion strength and coefficient friction of Re-Ir thin films were examined. The Re-Ir coating technique has received intensive attention in the coating processes field because of promising features, such as hardness, high elasticity, abrasion resistance and mechanical stability that result from the process. Re-Ir coating technique has also been applied widely in industrial and biomedical applications. In this study, WC molding core was manufactured, using high-performance precision machining and the effects of the Re-Ir coating on the surface roughness.

• Journal of the Earthquake Engineering Society of Korea
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• v.28 no.4
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• pp.183-191
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• 2024

Accurate seismic vulnerability assessment requires high quality and large amounts of ground motion data. Ground motion data generated from time series contains not only the seismic waves but also the background noise. Therefore, it is crucial to determine the high-pass cut-off frequency to reduce the background noise. Traditional methods for determining the high-pass filter frequency are based on human inspection, such as comparing the noise and the signal Fourier Amplitude Spectrum (FAS), f² trend line fitting, and inspection of the displacement curve after filtering. However, these methods are subject to human error and unsuitable for automating the process. This study used a deep learning approach to determine the high-pass filter frequency. We used the Mel-spectrogram for feature extraction and mixup technique to overcome the lack of data. We selected convolutional neural network (CNN) models such as ResNet, DenseNet, and EfficientNet for transfer learning. Additionally, we chose ViT and DeiT for transformer-based models. The results showed that ResNet had the highest performance with R² (the coefficient of determination) at 0.977 and the lowest mean absolute error (MAE) and RMSE (root mean square error) at 0.006 and 0.074, respectively. When applied to a seismic event and compared to the traditional methods, the determination of the high-pass filter frequency through the deep learning method showed a difference of 0.1 Hz, which demonstrates that it can be used as a replacement for traditional methods. We anticipate that this study will pave the way for automating ground motion processing, which could be applied to the system to handle large amounts of data efficiently.

• International Journal of Highway Engineering
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• v.13 no.1
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• pp.239-249
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• 2011

The behavior of the fiber reinforced concrete (FRC) base under environmental loads was analyzed numerically as a fundamental study to develop a high structural and functional performance composite pavement system in which the base was formed using FRC and the asphalt or cement concrete surface was placed on it. A two-dimensional finite element model of the FRC base was developed and the sensitivity study was performed with the variables including slab thickness of base, thermal expansion coefficient, elastic modulus, and tensile and compressive strengths. The crack spacing and crack width were selected as representatives of the base behavior. The effects of the selected variables on the crack spacing and crack width were analyzed and the sensitive variables were determined. The results of this study could be useful to determine the optimal material properties of the FRC base for combining well with the surface materials.

• The Journal of the Acoustical Society of Korea
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• v.21 no.3
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• pp.285-292
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• 2002

One of the problems that should be solved in Text-To-Speech (TTS) is discontinuities at unit-joining points. To cope with this problem, a smoothing method using a low-pass filter is employed in this paper, In the proposed soothing method, a filter coefficient that controls the amount of smoothing is determined according to contort information to be synthesized. This method efficiently reduces both discontinuities at unit-joining points and artifacts caused by undesired smoothing. The amount of smoothing is determined with discontinuities around unit-joins points in the current synthesized speech and discontinuities predicted from context. The discontinuity predictor is implemented by CART that has context feature variables. To evaluate the performance of the proposed method, a corpus-based concatenative TTS was used as a baseline system. More than 6075 of listeners realized that the quality of the synthesized speech through the proposed smoothing is superior to that of non-smoothing synthesized speech in both naturalness and intelligibility.